1. Field of the Invention
This invention relates to the sintering of lead concentrates and, more particularly, to an improved process for sintering lead concentrates using programmed oxygen enrichment coupled with the use of fog nozzles in selected wind boxes to obtain the highest permissible sintering temperatures for increased production while achieving a relatively high degree of desulfurization.
2. The Prior Art
For the past several decades, the pyrometallurgical production of lead from lead sulfide concentrates has been accomplished by (1) the autogenous updraft sintering of the lead sulfide concentrates for sulfur removal followed by (2) blast furnace smelting of the sinter using coke as the fuel. With particular reference to the schematic illustration of a conventional sintering process shown in FIG. 1, the sintering operation takes place in a conventional sintering machine wherein an initial, thin layer (about 30 millimeters) of balled mix (having a ratio of about 137 kg concentrates, 76 kg recycle slag, and 263 kg return sinter) is laid on the moving grate of the sinter machine. The grate is continuous and moves to the right at a rate of about 1 meter per minute. This initial layer is heated to ignition temperature by downwardly fired oil or gas burners. The combustion gases from the burners are drawn downwardly through the layer and removed.
Immediately following the ignition position, the remainder of the mix bed is spread on top of the ignition layer to a total height of about 280 millimeters. Air is blown upwardly through both the hot, ignition layer and the overlying fresh mix. Heat from the hot, ignition layer is sufficient to commence ignition of the adjacent material with the resulting hot combustion gases passing upwardly through the balance of the fresh mix. The upwardly moving, hot gases, depleted in oxygen, rise from the ignition zone to enter the balance of the fresh mix, preheating and drying the same. As the bed moves to the right, the region of ignition forms a reaction band that moves upwardly through the bed resulting in a band of reacting material located generally diagonally through the moving bed. The thickness of the reacting band depends upon the reaction rate. At a point a few minutes after ignition, air rising upwardly through the grate is heated as it passes through the reacted sinter and cools the same prior to entering partially reacted mix and fresh mix to react therewith, passing thence into additional unreacted material which is dried and preheated by the reaction gases.
The gas issuing from the top of the bed contains oxides of sulfur and is collected and sent to the acid plant where the sulfur oxides are converted into sulfuric acid. Approximately 84 percent of the sulfur is removed by this conventional sintering process.
Great care must be taken to prevent excessive temperature rise in the sintering process since temperatures above about 1300 K. result in the production of excessive amounts of liquid oxides which plug the interstices and impede the passage of oxidizing gases. Importantly, the initial composition of the charge to the sintering machine is carefully predetermined in order to control the temperature that is reached in the sintering process. For example, the relatively high ratio of cooled, return sinter (263 kg) assures that the richness of the charge will be sufficiently diluted to maintain temperatures below the 1300 K. limit. The cooled sinter also (1) provides the necessary porosity for the mix and (2) acts as a heat sink. The recycled slag (76 kg) serves as a flux for the process.
It would, therefore, be an advancement in the art to provide improvements in the process for sintering lead concentrates. It would also be an advancement in the art to increase the percentage of sulfur removed from the sinter. Another advancement in the art would be to provide improvements in the process for sintering lead concentrates at an increased rate of production. Such a novel, improved process is disclosed and claimed herein.